In synthesizing a new molecule that mimics the nickel-iron (NiFe) hydrogenase enzyme, a team of researchers from University of Illinois Urbana-Champaign (www.illinois.edu) may have uncovered a promising alternative to the platinum-based catalysts typically used in the electrolysis of water to produce hydrogen. With the new molecule, the scientists have uncovered a previously unreported mechanism in the hydrogen evolution reaction (HER).
In work published in Nature Communications, the team reports that they have, for the first time, demonstrated that both NiI and NiIII paramagnetic states are accessed during catalytic hydrogen evolution, which is believed to be indicative of the specific chemistry of NiFe hydrogenases.
While other nickel complexes have been investigated for electrocatalytic hydrogen production, their reaction intermediates and activity did not support an efficient reaction. The key to the new catalyst’s efficiency is the formation of the paramagnetic intermediate species at the nickel center. The intermediates’ unpaired electron and short lifespan mean that the HER proceeds more efficiently than with other nickel-based catalysts. The molecule’s unique behavior when compared to other catalysts is due in part to a carbon-hydrogen bond located near that nickel center, which is cleaved and mended during the reaction, helping to stabilize the paramagnetic species. Furthermore, the molecule was outfitted with a specialized ligand based on 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane that could support the paramagnetic states and their seemingly challenging behavior — a direct mirror of the cysteine ligands found in NiFe hydrogenases.
The new catalyst exhibited high turnover frequencies for hydrogen production in the presence of trifluoroacetic acid. The team hopes that this work will spur deeper research into bio-inspired organometallic complexes.